1. Field of the Invention
The field of art to which this invention pertains is "Thin Film Circuits", and in particular to thin film circuits for forming resistor and capacitor elements by deposition on a planar substrate of insulating material.
2. Description of the Prior Art
In tantalum thin film technology, tantalum nitride films are conventionally used for resistors, and .beta.-tantalum films are conventionally used for capacitors. The production of integrated RC-thin film circuits takes place, for example, in such a manner that the capacitors are created from .beta.-tantalum on one substrate, the resistors are created from tantalum nitride on another substrate, and that, finally, both substrates are joined together. If one desires to produce RC-networks on a common substrate, a reciprocal disturbance arises in the production processes of the resistors and capacitors, which can be eliminated through additional measures.
A significant problem exists in that sandwich films of tantalum nitride and .beta.-tantalum cannot be selectively etched. It was, therefore, initially proposed that intermediary films of tantalum pentoxide (U.S. patent application Ser. No. 409,656 now U.S. Pat. No. 3,406,043; ) or aluminum (U.S. patent application Ser. No. 409,890 now U.S. Pat. No. 3,387,952 ) be inserted between the tantalum nitride film and the .beta.-tantalum film. Through the utilization of tantalum pentoxide, which normally is an insulator, the electrical losses of the circuit are, however, greatly increased, whereas the selective etching of tantalum over aluminum is problematic. Moreover, the procedures become complicated through the utilization of three films in each case.
An improved solution to this problem is described in the journal "Proceedings, 1970, Electric Components Conference", Washington, Pages 602-612. According to this known method .beta.-tantalum is initially sputtered, etched, and partially formed, whereupon tantalum nitride is deposited over the entire surface. The oxide film created by the formation of the .beta.-tantalum serves as an etching barrier in the etching of the tantalum nitride, so that tantalum nitride can be removed from the desired places without causing the .beta.-tantalum underneath to be also etched away. In the continued course of the known method of production, the annealing required for the stabiliztion of the resistors impairs the dielectric characteristics of the tantalum pentoxide, which must be restored by means of a second formation of the capacitor zones.
The large number of method steps required in this known procedure, however, has a negative effect on the yield of the networks, and thereby on the economy. The production of thin film-RC-networks on a common substrate for resistors and capacitors would be much easier if one could produce resistors and capacitors with the required features, instead of from two primary films, from a single primary film. This problem is discussed in the above-mentioned journal on Page 602, in the second paragraph of the right column. It is also stated therein, that, on the basis of known techniques, a solution of this problem was not possible, or only possible with insufficient preciseness.
In U.S. patent application Ser. No. 408,100, now U.S. Pat. No. 3,955,039 sputtered Al-Ta-alloy films with approximately 2 to 20 atom percent tantalum in aluminum are indicated, which are distinguished by their high oxidation stability and great anodization sparking potential.